U.S. Pat. No. 5,184,682 describes a known rod made from a composite material which may be pulled or pushed into a well or in a tube placed in a well. A line, for example an electric line, is embedded in the rod and allows a measuring and/or servicing device fastened to the end of the rod to be connected. However, to perform a series of measurements over the total length of the production drain hole, the measuring device has to be moved by acting upon the rod located in the drain hole by winding or unwinding from a reel.